1. Field of the Invention
This invention relates to light valves for optical projection of images generated electronically on a fluid layer, and more particularly to light valves having an improved disk assembly and to an improved method of assembling the disk assembly.
2. Description of the Prior Art
One form of light valve suitable for optical projection of electronically generated images onto a remote display surface comprises an evacuated envelope containing an electron gun in alignment with a transparent disk. The disk is rotated through a reservoir of light modulating fluid to deposit a continuously replenished layer of fluid on the disk surface. An electron beam, generated by the electron gun, is directed through electrostatic beam deflecting and focusing means and is scanned across a portion of the light modulating fluid layer so as to selectively deform the layer. The fluid deformations thus formed constitute diffraction gratings which, in conjunction with a Schlieren optical system, selectively control passage of light from a light source through the disk and through an output window in the light valve envelope in order to create visible images at a remote display surface on which the light impinges.
Light valves of the type described have hitherto operated satisfactorily only for limited periods of time. Although the light modulating fluid is free from particulate contamination at the outset of light valve operation, a buildup of contamination occurs as operation of the light valve progresses. This contamination is due in part to the wear of moving parts within the light valve, as well as to the presence of impurities. In addition, some particles may be formed as a result of massive damage to fluid molecules caused by heavy electron or ion bombardment. Eventually, this contamination may reach a level which results in the deterioration of the displayed image.
To overcome the problem of contamination, it has been proposed in H. E. Towlson U.S. Pat. No. 3,489,940, assigned to the same assignee as the present application, to provide apparatus for hydrodynamically isolating the light modulating fluid layer on the disk from the contaminated, particulate-carrying sump fluid in order to prevent the sump fluid from mixing with the fluid layer on the disk surface. By situating a baffle plate in close parallel proximity to one side of the disk and dispensing fluid from a channel of predetermined configuration on the side of the baffle plate facing the disk, a low fluid flow rate is sufficient to maintain fresh filtered fluid within the entire region between the baffle plate and the disk. Only fresh filtered fluid is thus picked up by the disk even though the region between the baffle plate and the disk is situated within the sump.
In the device shown in said patent, and more particularly in the present commercial form of this device, the disk is mounted for rotation on bearing means supported on a disk drive support plate, which also supports the drive system for the disk. The disk drive support plate is a stamped sheet metal plate having feet which are springloaded against a face plate. The baffle plate is positioned between the disk and the disk drive support plate, which is parallel to the disk and baffle plate, but extends only partially over the disk. A light output window has one of its sides positioned in close parallel proximity to the other side of the disk and maintained a capillary distance therefrom by spacers in the form of frit dots fused to the window. The baffle plate is supported on spacers, each of which includes a laterally extending foot engaged with, and spring biased against, the other side of the window.
A number of problems have been faced in the assembly of this prior art device. Because the oil distribution gap between the disk and the baffle plate needs to be thin (about 0.010 inch) to prevent oil flow in from the surrounding sump area, the tolerances on all the parts, i.e., the light output window, the disk, the baffle plate and the spacer feet, are critical and must be held closely to prevent the disk from hitting the baffle plate. As the disk is positioned edgewise into the gap between the baffle plate and the light output window, there is the danger that the disk will rub against the edge of the baffle plate and cause a slight scratch or bruise on the surface of the disk, resulting in the rejection of the disk for use in the light valve apparatus.
After the disk is inserted in the gap, the disk drive support plate is positioned over the baffle plate and disk and is set into place. During this step, the exposed surface of the disk is frequently contaminated by particulate material falling on the disk. It is then necessary to disassemble the apparatus, reclean the disk, and reassemble the apparatus. Often, this procedure must be repeated several times. As a result, the time and cost of assembly is substantially increased.
Because the disk drive support plate is stamped from a metal sheet and has integral depending feet which are engaged against the face plate of the envelope of the light valve device, it has sufficient flexibility that accurate pitch spacing between the gear reduction system carried on the support plate and the ring gear mounted on the peripheral edge of the disk is difficult to maintain. This often leads to erratic disk motion.